Gain control circuits



Patented Sept. 20, 1938 UNITED STATES anni PATENT OFFICE TelephoneLaboratories,

Incorporated, New

York, N. Y., a corporation of New York Application May 28, 1937, SerialNo. 145,208

10 Claims.

This invention relates to gain control circuits for transmission linesand particularly to pilot wire gain control circuits for transmissionlines.

One object of the invention is to provide a gain control circuit forcontrolling the gain at a station on a transmission line by a pilot pathextending to an associated station that shall have the setting of thegain adjusted at the associated station.

Another object of the invention is to provide a gain control circuithaving a pilot path extending between unattended and attended stationson a transmission line that shall adjust the gain at an unattendedstation by changing the resistance of the path at an attended station.

Another object of the invention is to provide a gain control circuithaving a pilot line extending between unattended and attended stationson a transmission line with a high temperature coefiicient resistance atthe unattended station under control of the pilot line for controllingthe gain at the unattended station that shall have the resistance of thepilot line adjusted at the attended station to set the gain effected atthe unattended station.

0n transmission lines, as for example, a carrier cable transmissionline, it is necessary to place repeater or gain control stations atintervals along the cable. These stations may be of the type'disclosedin the patent to Fred A. Brooks, No. 2,075,975, April 6, 1937, if sodesired. Some of the gain control stations are attended and other of thegain control stations are unattended. At times it is desirable to changethe setting of the gain at a repeater station. At an attended stationthe level at which the gain is effected may be conveniently adjustedwhereas at an unattended repeater station it has heretofore beeninconvenient to adjust the setting of the gain controlling apparatuswithout sending a repeater attendant to the station.

According to the invention, it is proposed to adjust the setting oi thegain at an unattended station from an attended station without theaddition of any extra control circuit between the two stations. Thus theattendant at any attended station may not only control the setting ofthe gain at the attended station but may also control the setting of thegain at an unattended station.

A cable carrying a large number of lines comprising transmissioncircuits may have attended and unattended stations thereon. The attendedgain control station will be vprovided with a pilot path extending fromthe unattended station to an attended station. The pilot path may beapair ci wires in the cable which serve for transmission purposes or maybe a separate pair of wires in the cable. The pilot path in one instancemay serve as a part of a bridge at the unattended station. The bridgemay operate a galvanometer control mechanism of the type disclosed inthe patent to I. G. Wilson, No. 2,086,105, July 6, 1937, for controllingthe gain of an amplier orl may control galvanometer control mechanism ofthe type disclosed in the patent to F. A. Brooks, N o. 2,075,975, April6, 1937. The pilot path is subjected to the same temperature changes asthe transmission line or lines whose gain is to be controlled. 'Iheresistance variation in the pilot path according to temperature changesgovern a bridge circuit which in turn governs the galvanometer controlmechanism to govern the gain control amplifier at the unattendedstation.

In order to permit setting of the gain at the unattended station fromthe attended station, an adjustable resistance element is inserted inthe pilot path at the attended station. The adjustable resistance isvaried by the attendant at the attended station to change the setting ofthe bridge at the unattended station and accordingly to adjust thesettingof the gain at the unattended station.

In a modication of the invention, the pilot path may be supplied by asource of current for heating a coil at the unattended station. The coilat the unattended station controls the heating oi elements of silversulphide or boron, which have a high temperature coefficient oiresistance. The elements having a high temperature coelicient ofresistance are inserted in the control circuit of the gain controlamplier at the unattended station. The resistance of the pilot pathwhich controls elements having high temperature coeicients of resistanceis adjusted at the attended station in the same manner as above setforth to adjust the setting of the gain at the unattended station.

In the accompanying drawing, Fig. l is a diagrammatic view of a gaincontrol circuit constructed in accordance with the invention;

Fig. 2 is a modification oi the gain control circuit shown in Fig. 1 ofthe drawing; and

Fig. 3 is a modification of the gain control circuit shown in Fig. 1 ofthe drawing, wherein a resistance element having a high temperaturecoeicient of resistance is employed to control the gain.

Referring to Fig. 1 of the drawing, a transmission line comprisingconductors l and 2 is shown, having two gain control stations 3 and 4connected thereto. The conductors l and 2 forming the transmission linemay be a pair of wires in a cable containing many other transmissionlines controlled by the apparatus at the gain control stations. Thestation 3 is assumed to be an attended gain or repeater station and thestation 4 is assumed to be an unattended gain or repeater station. Anamplifying repeater 5, which is preferably of the thermionic type, isprovided at the attended station 3 and a similar amplifying device 6 isprovided at the unattended gain control station 4. The amplifying device5 at the attended station 3 is governed by control mechanism 'I whichmay be of the type disclosed in the F. A. Brooks patent, No, 2,075,975or of the type disclosed in the patent to I. G. Wilson,

No. 2,086,105, July 6, 1937. It is understood that the control mechanismat the station 3 is governed by a pilot line (not shown) of any suitabletype.

10 The unattended station 4 which controls the gain of an amplifyingdevice 6 is governed by a bridge circuit 8. trolled by a pilot path 9extending between the two stations 3 and 4. The pilot path 9 extending15 between the attended and unattended stations forms a part of thebridge circuit. As illustrated,

the pilot path 9 comprises a direct current path on the transmissionconductors l and 2 which form the transmission line. The bridge circuit8 is connected to the conductors I and 2 by means of a filter I8comprising series inductive elements II and I2 and a condenser I3. Thefilter I serves to permit the flow of direct current and to insureagainst a transmission of any signal currents to the bridge circuit. Asimilar filter I4 comprising inductance elements I5 and IS and acondenser I7 is provided at the distant terminal of the pilot path 9,located at the attended gain control station 3. The end of the pilotpath 9, located at the attended station, is terminated by means of anadjustable resistance element I8. The adjustable resistance element I8is under the control of the operator at the attended station and servesto adjust or set the level about which the regulation of the gain at theunattended station is affected. l

The bridge circuit 8,comprises resistance elements I9, 20, 2|, 22, 23and 24. The resistance element 24 is adjustable for rebalancing thebridge circuit after each operation of the apparatus at the unattendedstation. Automatic galvanometer mechanism 25 of the type referred to inthe above-mentioned patent to F. A. Brooks, No. 2,075,975, is connectedacross two opposite vertices of the bridge 8. A battery 26 is connectedacross the other two vertices of the bridge 8. The automaticgalvanometer mechanism 25 operates a shaft 27, which in turn drives therotor 28 of a master motor 29. A stator win-ding 30 of the master motor29 is connected to a suitable source of alternating current (not shown).The shaft 27 is also connected to an arm 3| controlling the resistance24 by means of bevel gear wheels 32 and a gear box 33 containingsuitable change gears.

The rotor winding ofthe rotor 28 is connected to the rotor winding of arotor 34 on a service motor 35. The service motor 35 is provided with astator winding 36 connected to the same source of alternating currentconnected to the stator winding of the main motor 29. Other smallerservice motors (not shown) may be connected in parallel to the mainmotor 29, as indicated in the drawing. The rotor 34 of the service motor35 is connected by a shaft 37 to a gear box 38, which controls the gainof the amplifying device 6 in the manner disclosed in theabove-mentioned patent to F. A. Brooks, No. 2,075,975.

In the apparatus above disclosed, a change in temperature on thetransmission conductors I and 2 will cause not only a change in theattenuation of the transmission line but also a change in the resistanceof the pilot path 9. The change in the resistance of the pilot path 9will unbalance the bridge circuit 8 and operate the auto- The bridgecircuit 8 is conv matic galvanometer mechanism 25 for changing the gainat the unattended station by means of the amplifying device 6 to correctfor the change in the line attenuation. At this time the adjustableresistance element 24 is varied to rebalance the bridge circuit. It isnecessary at times to adjust the setting of the gain control apparatusat the unattended station. This change of the setting of the gain isaffected by adjusting the resistance element I8 at the attended station3. The resistance element I8 as before set forth forms the terminal ofthe pilot path 9 for the unattended station.

Referring to Fig. 2 of the drawing, a system very similar to the systemshown in Fig. 1 is illustrated, having the gain control apparatus at theunattended station controlled by a pilot path having two conductorspositioned adjacent to the transmission line. Like parts in Fig. 2 tothose shown in Fig. 1 will be indicated by similar reference characters.

The pilot path for the bridge 8 at the unattended station 4 comprisestwo conductors 40 and 4I, which are preferably a pair of wires in aposition adjacent to the pair of wires I and 2 forming the transmissionline. The pilot path comprising the conductors 40 and 4I is terminatedat the attended station by means of an adjustable resistance I8, whichserves to effect adjustment of the gain at the unattended station 4. Thecircuits shown in Fig. 2 operate in the same manner as the circuitsshown in Fig. 1 and a detailed description thereof is deemedunnecessary.

Referring to Fig. 3 in the drawing, a transmission line comprisingconductors 45 and 49 is provided with an attended gain control station47 and an unattended gain control station 48. The attended gain controlstation 47 is provided with an amplifying device 49 and the unattendedstation 48 is provided with an amplifying device 50. The amplifyingdevices 49 and 50 may be of the type referred to in describing theamplifying devices and 6 in Fig. 1 of the drawing. The amplifying device49 at the attended station 47 may be governed by control mechanism 5Isimilar to the control mechanism 'I referred to when describing thecircuits shown in Fig. 1 of the drawing.

The gain control device 50 shown in Fig. 3 of the drawing is governed bya feedback circuit comprising a suitable equalizer 52, resistanceelement 53 having a high temperature coefficient of resistance and aresistance element 54. The resistance element 53 may be composed ofsilversulphide, barium, or any other suitable material. The resistanceelement 53 is mounted with a heating coil 55 within a suitable oven 55.The heating coil 55 terminates a pilot line 57 which extends from theunattended station 48 to the attendedv station 47. At the attendedstation 47, an adjustable resistance element 58 is provided forcontrolling the setting of the gain of the amplifying device 59 from theattended station. Thus by adjusting the resistance element 58 it ispossible to adjust the level at which the gain at the unattended station43 is regulated by means of the pilot line 57. A battery 59 which may belocated at any suitable point is provided for heating the coil 55.

Changes in temperature to which the transmission line comprising theconductors 45 and 48 is subjected not only vary the attenuation of thetransmission line but also vary the resistance of the pilot line 57.Change in the resistance of the pilot line 51 changes the heating of thesilversulphide element 53 by the heating coil 55. ations in theresistance of the silver-sulphide element 53 varies the feedback circuitfor the Aamplifying device 50. The feedback circuit is connected to theinput circuit of the amplifying device 50 by means of the resistanceelement 54, as shown in the drawing.

Modifications in the circuits and in the arrangement in location ofparts may be made within the spirit and scope of the invention and suchmodications are intended to be covered by the appended claims.

What is claimed is:

1. In a signal transmission line having an attended gain control stationand an unattended gain control station thereon, a gain control pathextending between said stations, gain control means in the line at theunattended stations, means controlled by the resistance variations ofsaid path to govern said gain control means, and means located at saidattended station for controlling said path to govern the setting of saidgain control means.

2. In a signal transmission line having an attended gain control stationand an unattended gain control station thereon, a gain control pathextending between said stations, a gain control amplier located at saidunattended station, means controlled according to the resistancevariations of the path to govern the gain of said amplier at theunattended station, and means located at said attended station foradjusting said path to govern the setting of the gain at the unattendedstation.

3. In a signal transmission line having two separated stations thereon,a gain control amplifier at one of said stations, a gain control pathextending between said stations and having a resistance variationaccording to temperature Variations, means controlled by said path forgoverning the gain of said amplifier according to the resistancevariations of the path, andan adjustable resistance element in said pathand located at a distance from said amplifier for adjusting the settingof the gain of said amplifier.

4. In a signal transmission line having attended and unattended gaincontrol stations thereon, a gain control amplifier-at the unattendedstation, means comprising a bridge circuit for governing the operationof said amplifier, pilot wire means extending between said stations andincluded in one arm of said bridge circuit for controlling the gain atthe unattended station, and resistance means at the attended station forvarying the resistance of said pilot wire means to control the settingof the gain of the amplifier at the unattended station.

5. In a signal transmission line, having attended and unattended gaincontrol stations thereon, a gain control amplier at each of saidstations, a bridge circuit at the unattended station, means controlledby said bridge for controlling the amplier at the unattended station, apilot path extending between the two stations and included in one arm ofsaid bridge circuit for controlling the bridge to govern the gain at theunattended station, and means at the attended station for varying theresistance of said pilot path to control the setting of the bridgecircuit and the control means at the unattended station.

Vari- 6. In a signal transmission line having an attended gain controlstation and an unattended gain control station thereon, a gain controlpath extending between said stations, a gain control amplier located atsaid unattended station, a bridge. circuit having said path includedtherein in order to be controlled according to the resistance variationsof the path, means controlled by said bridge for governing the gaineffected by said amplifier, and means comprising a variable resistanceelement included in said path at the attended station for controllingthe setting of the bridge at the unattended station.

7. In a signal transmission line having an attended gain control stationand an unattended gain control station thereon, a gain control path`extending between said stations, a bridge cir- Cuit vhaving said pathincluded therein in order to be controlled according to the resistancein variations of said path, means controlled by said bridge forgoverning the gain on the transmission line at the unattended station,and means located at the attended station for varying the resistance ofthe pilot path to change the setting of said bridge.

8. In a signal transmission line having an attended gain control stationand an unattended gain control station thereon, a pilot line extendingbetween the two stations and having a source of current includedtherein, a resistance element at the unattended station having a hightemperature coefcient of resistance, means controlled by said pilot lineaccording to the temperature thereof for governing the temperature cfsaid resistance element, means controlled by said resistance element forgoverning the gain on the transmission line at the unattended stationand a variable resistance element in the pilot line at the attendedstation for varying the pilot line resistance to control the setting ofthe gain at the unattended station.

9. In a signal transmission line having attended and unattended gaincontrol stations thereon, a pilot line extending between said stations,a heater coil connected to the pilot line at the unattended station, aresistance element having a high temperature coeiicient of resistanceheated by said coil, means controlled by said resistance element forgoverning the gain on the transmission line at the unattended station,and

a variable resistance element in said pilot line at the attended stationfor controlling the setting of the temperature of the resistanceelement.

10. In a signal transmission line having an attended gain controlstation and an unattended gain control station thereon, a pilot lineextending between the two stations, a source of current connected tosaid pilot line, a gain control amplifier at the unattended station, aresistance element at the unattended station having a high temperaturecoefficient of resistance, means controlled by the variations inresistance of said pilot line with temperature changes for controllingthe heating of said resistance element, means controlled by saidresistance element for governing the operation of said amplifier, and avariable resistance element in said pilot line at the attended stationfor varying the pilot line resistance to control the setting of saidamplifier.

IRA G. WILSON.

